1. Field of the Present Invention
The present invention relates to an optical access network apparatus and its data signal sending method, and more particularly to an OLT (Optical Line Terminal) in an optical access network and a data signal sending method for enabling a subscriber terminal to send a data signal via the OLT to a network.
2. Description of the Related Art
An xDSL (x-Digital Subscriber Line) is the generic term of ADSL (Asymmetric Digital Subscriber Line), HDSL (High-bit-rate DSL), RADSL (Rate-Adaptive DSL), SDSL (Symmetric DSL), and VDSL (Very-high-bit-rate DSL). This xDSL is a modem technique allowing for the fast packet communications at several tens Megabits/sec at maximum, using the existing subscriber line (ordinary telephone cable made of copper wire) as a transmission line. Due to the introduction of communication services employing the xDSL, a high-speed and always-connected internet access network has become popular and widely spread.
However, as the xDSL technology involves the packet communication using the telephone cable, it has a problem that the transmission characteristics and the data transmission speed are affected by the length of the telephone cable, the characteristics of the telephone cable, and the peripheral environmental conditions of wiring path of the telephone cable from a telephone switching office to the subscriber's premises.
Thus, an access network employing the optical technologies has been widely spreading, instead of the access network employing the xDSL technology. The access network employing the optical technologies is an optical access network so called an EPON (Ethernet Passive Optical Network) which employs the Ethernet technologies and realizes the packet communication through an optical cable connected to the subscriber's premises. The PON technology is recommended in the IEEE (The Institute of Electrical and Electronics Engineers, Inc.) 802.3ah.
The optical access network by the EPON is composed of an OLT (Optical Line Terminal) that is installed in the switching center of a communication common carrier, and an ONU (Optical Network Unit) that is installed in the subscriber's premises. This optical access network is constructed by laying one optical fiber cable to an area in which plural subscribers' premises are locating, connecting a splitter as an optical coupler to the optical fiber cable for splitting an optical path into a plurality of optical paths, and connecting each of split optical cables to respective subscriber's premises. The optical access network can provide the subscriber with the packet communications of wider band and higher quality than the access network with the metallic cable such as the telephone cable. Particularly, the optical access network is most suitable for an application such as the moving picture contents distribution services.
On the other hand, in the communications network, it is necessary to secure the high speed and high quality communications, and it is also important to maintain the reliability of the network by increasing the tolerance or taking measures against the line disturbances. Therefore, the techniques for the dual or redundant configuration of the network have been developed in the optical access network. One of those techniques is disclosed in Japanese Patent Application Laid-Open No. 2003-111116 as a system which performs redundant line selection in order to equalize the frequency of line usage. Also, in Japanese Patent Application Laid-Open No. 2003-318933, a proposal has been made for a system which has a redundant configuration of the active line and the standby line, and diverts a part of data to the standby line when amount of the input data has exceeded beyond the band assured by the active line.
The configuration of an optical access network based on the functions of the conventional OLT will be described below.
The conventional OLT has a SNI (Service Node Interface) port corresponding to each PON (Passive Optical Network) interface for connection to the network. The OLT accommodates a plurality of PON interfaces (or mounts a plurality of PON interface boards), and their respective SNI ports are connected corresponding one to one to the ports of an L2 (layer 2) switch provided in the network. That is, in a case where the OLT mounts twelve PON interface boards and provides twelve SNI ports, the twelve SNI ports are connected to the L2 switch of the network.
FIG. 29 is a system block diagram representing the essence of an example of the conventional optical access network of non-concentrate type.
An OLT 101 of the conventional optical access network comprises a control board 102 for controlling the entire apparatus (the OLT 101), and n (n is arbitrary integer) PON interface (PON I/F) boards 1031, 1032, . . . and 103n. This conventional optical access network is composed of a network element of subscriber side and a network element of network side. The network element of subscriber side comprises the optical fiber cables 1041, 1042, . . . and 104n connecting to the respective PON interface boards 1031, 1032, . . . and 103n in the OLT 101, the 1×N splitters 1051, 1052, . . . and 105n for splitting each of the optical fiber cables 1041, 1042, . . . and 104n into N (N is arbitrary integer) split optical cables for subscribers, not shown, and n×N ONUs 10611 to 1061N, 10621 to 1062N, . . . and 106n1 to 106nN connected to the respective 1×N splitters 1051, 1052, . . . and 105n through the split optical cables. And the network element of network side is configured such that the SNI ports 1081, 1082, . . . and 108n, which are interfaces on the network side of the PON interface boards 1031, 1032, . . . and 103n in the OLT 101, are connected to an L2 switch (L2 SW) 109 of the network.
In the configuration of the conventional optical access network in FIG. 29, data is transmitted or received between the subscriber terminal, not shown, and the network on the paths as indicated by the arrow 1111, 1112, . . . and 111n. That is, data is transmitted or received via the L2 switch 109, the SNI ports 1081, 1082, . . . and 108n of the OLT 101, the PON interface boards 1031, 1032, . . . and 103n, the optical fiber cables 1041, 1042, . . . and 104n and the ONUs 10611 to 1061N, 10621 to 1062N, . . . and 106n1 to 106nN.
On the other hand, FIG. 30 is a system block diagram representing the essence of an example of the conventional optical access network of concentrate type. The same parts are given the same numerals throughout FIGS. 29 and 30, and the explanation of the same parts is omitted properly.
An OLT 121 of the conventional optical access network as shown in FIG. 30 comprises a multiplex board 122 for controlling the entire apparatus (the OLT 121) and multiplexing the data from the subscriber terminals, and n PON interface boards 1031, 1032, . . . and 103n. This conventional optical access network is composed of a network element of subscriber side and a network element of network side. As the configuration of the network element of subscriber side is the same as that shown in FIG. 29, the explanation is omitted. The network element of network side is configured such that an SNI port 123 that is an interface on the network side of the multiplex board 122 is connected to the L2 switch 109.
In the configuration of the conventional optical access network as shown in FIG. 30, data is transmitted or received on the paths as indicated by the arrow 131 and arrow 1321, arrow 131 and arrow 1322, . . . , and arrow 131 and arrow 132n between the subscriber terminal, not shown, and the network. That is, data is transmitted or received via the L2 switch 109, the SNI port 123 of the OLT 121, the PON interface boards 1031, 1032, . . . and 103n, the optical fiber cables 1041, 1042, . . . and 104n and the ONUs 10611 to 1061N, 10621 to 1062N, . . . and 106n1 to 106nN.
In FIGS. 29 and 30, the section of the optical fiber cable between the PON interface boards and the ONUs is called “a PON section”.
In the PON system for the optical access network, some measures for providing a duplex system that enables the switching of the PON section at the time of line disturbances have been conventionally proposed. However, no system has been proposed yet for protecting a portion relating to the PON interface boards and the SNI ports at the time of fault. Thereby, the following problems arise.
A first problem is that the cost of facility investment is increased when redundant configuration facilities are provided for the network element of network side in the conventional optical access network of non-concentrate type.
The conventional OLT 101 of non-concentrate type comprises the SNI ports 1081, 1082, . . . and 108n corresponding to the PON interface boards 1031, 1032, . . . and 103n, as shown in FIG. 29. Therefore, various facilities are required doubly by simply making the apparatus duplex, so that the cost of equipment is increased.
A second problem is that the conventional OLT 201 of concentrate type cannot separate the data traffic for transmission depending on the type of subscriber (or subscriber class). To assure the service quality for the respective subscribers, it is required to separate the data traffic for transmission depending on the subscriber class.
The conventional OLT 201 of concentrate type concentrates the data traffic for the PON interface boards 1031, 1032, . . . and 103n in the multiplex board 122 with a single SNI port 123, as shown in FIG. 30, whereby the duplex provision of multiplex board is possible for realizing a redundant configuration. However, the redundant configuration of the multiplex board will cause the complex settings of internal control and troublesome operation for quality assurance in assuring the quality of data depending on the subscriber class.
A third problem is that the degree of freedom of setting a path to the network for each subscriber or service is lowered in the both forms of the non-concentrate type and the concentrated type. That is, there are physical separation and logical separation for routing the data corresponding to each subscriber. The physical routing is generally made by the physically independent SNI ports, and the logical routing is generally made by a general VLAN (Virtual Local Area Network) tag. However, these routing methods must accord with a management scheme dependent upon the topology of the OLTs 101 and 121 (FIGS. 29 and 30) connecting to the network.